linux-kernel - Re: [PATCH 4.19 18/56] hv: utils: add PTP_1588

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Date:   Mon, 20 Dec 2021 21:49:32 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Pavel Machek <pavel@....cz>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        kernel test robot <lkp@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 18/56] hv: utils: add PTP_1588_CLOCK to Kconfig to
 fix build

On Mon, Dec 20, 2021 at 9:31 PM Pavel Machek <pavel@....cz> wrote:
> > From: Randy Dunlap <rdunlap@...radead.org>
> >
> > [ Upstream commit 1dc2f2b81a6a9895da59f3915760f6c0c3074492 ]
> >
> > The hyperv utilities use PTP clock interfaces and should depend a
> > a kconfig symbol such that they will be built as a loadable module or
> > builtin so that linker errors do not happen.
> >
> > Prevents these build errors:
> >
> > ld: drivers/hv/hv_util.o: in function `hv_timesync_deinit':
> > hv_util.c:(.text+0x37d): undefined reference to `ptp_clock_unregister'
> > ld: drivers/hv/hv_util.o: in function `hv_timesync_init':
> > hv_util.c:(.text+0x738): undefined reference to `ptp_clock_register'
>
> This is bad idea for 4.19:
>
> > +++ b/drivers/hv/Kconfig
> > @@ -16,6 +16,7 @@ config HYPERV_TSCPAGE
> >  config HYPERV_UTILS
> >       tristate "Microsoft Hyper-V Utilities driver"
> >       depends on HYPERV && CONNECTOR && NLS
> > +     depends on PTP_1588_CLOCK_OPTIONAL
> >       help
> >         Select this option to enable the Hyper-V Utilities.
>
> grep -ri PTP_1588_CLOCK_OPTIONAL .
>
> Results in no result in 4.19. So this will break hyperv. No results in
> 5.10, either, so it is bad idea there, too.

Right, this doesn't work, but the bug does exist anyway, and could be
fixed by listing the dependency explicitly as

           depends on PTP_1588_CLOCK || PTP_1588_CLOCK=n

The PTP_1588_CLOCK_OPTIONAL was added as a shortcut to
avoid the odd Kconfig syntax that most developers struggle with understanding
at first.

         Arnd